Conventionally, a capacitive type dynamic quantity sensor such as the one shown in FIG. 7 is typically constructed by etching a substrate 10 such as a semiconductor substrate. The etching forms a trench in the substrate 10 to separate a movable portion including beam portions 22 and movable electrodes 24 from electrodes of fixed electrode groups 32, 42.
The beam portions 22 extend in a direction perpendicular to the Y direction in FIG. 7 and are spring-like in operation, as they deform in the Y direction with respect to a force applied thereon. The movable electrodes 24 also extend in a direction that is perpendicular to the Y direction and move in the Y direction along with the beam portions 22. The movable electrodes 24 have, for example, a comb-shaped configuration.
The comb-shaped electrodes of the fixed electrode groups 32, 42 are supported by and fixed on the substrate 10 to respectively face the movable electrodes 24.
According to the above described capacitive type dynamic quantity sensor, a total capacitance CS1 is formed in gaps D disposed between the movable electrodes 24 on the left side in FIG. 7 and the electrodes of the fixed electrode group 32, and a total capacitance CS2 is formed in gaps D disposed between the movable electrodes 24 on the right side in FIG. 7 and the electrodes of the fixed electrode groups 42. When a physical quantity such as acceleration is applied to the capacitive type dynamic quantity sensor, the capacitances CS1, CS2 vary with respect to an amount of the physical quantity. Therefore, the physical quantity is detected based on the variation of difference between the capacitances CS1, CS2.
In the above capacitive type dynamic quantity sensor, the fixed electrode groups 32, 42 and the movable portion including the beam portions 22 and the movable electrodes 24 are formed at the same time by etching the trench in the substrate 10. Therefore, a manufacturing error of width B is approximately the same relative to each of the beam portions 22 and the gaps D disposed between the movable electrodes 24 and the electrodes of the fixed electrode groups 32, 42. For example, as the widths B of the beam portions 22 increase in width, the gaps D disposed between the movable electrodes 24 and the electrodes of the fixed electrode groups 32, 42 decrease in width.
Accordingly, the manufacturing error causes variations of the widths B and the gaps D, and therefore characteristic non-uniformity of the capacitive type dynamic quantity sensor becomes large.
Incidentally, the characteristic non-uniformity of the capacitive type dynamic quantity sensor can be minimized by enlarging the widths B and the gaps D. However, the capacitances CS1, CS2 consequently decrease and sensor sensitivity also decreases.